Variation in carotid endarterectomy mortality in the Medicare population - Trial hospitals, volume, and patient characteristics

Context.-The North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Atherosclerosis Study (ACAS) demonstrated the efficacy of carotid endarterectomy (CEA) in reducing the risk of stroke and death in selected patients when surgery was performed in institutions whose participation depended on demonstrated excellence. Thirty-day mortality rates in the trials were very low: 0.6% in NASCET and 0.1% in ACAS. Objective.-To assess perioperative mortality among Medicare patients undergoing CEA in all nonfederal institutional settings. Design.-Retrospective national cohort study. Setting and Patients.-All 113 300 Medicare patients undergoing CEA during 1992 and 1993 in "trial hospitals" (those participating in NASCET and ACAS, n=86) and "nontrial hospitals" tall other nonfederal institutions performing CEAs, n=2613). Nontrial hospitals were stratified into terciles based on volume of CEAs performed. Main Outcome Measures.-Crude and adjusted perioperative (30 day) mortality rates. Results.-The perioperative mortality rate was 1.4% (95% confidence interval [CI], 1.2%-1.7%) at trial hospitals; mortality in nontrial hospitals was higher: 1.7% (95% CI, 1.6%-1.8%) thigh volume); 1.9% (95% CI, 1.7%-2.1%) (average volume); 2.5% (95% CI, 2.0%-2.9%) (low volume); (P for trend, <.001). In multivariate modeling, patients undergoing their procedures at trial hospitals had a mortality risk reduction of 15% (95% CI, 0%-31%) compared with high-volume nontrial hospitals, 25% (95% CI, 7%-40%) compared with average-volume hospitals, and 43% (95% CI, 25%-56%) compared with low-volume hospitals (P for trend, <.001). Conclusion.-Medicare patients' perioperative mortality following CEA is substantially higher than that reported in the trials, even in those institutions that participated in the randomized studies. Caution is advised in translating the efficacy of carefully controlled studies of CEA to effectiveness in everyday practice.